Types of Arguments

o     If Premises are True, the Conclusion must be True/Cannot be False

o     Deductive Argument:  Adding Premises is Unnecessary

o     Even if the Premises are True, the Conclusion could be False

  •       When Premises very Probably imply the Conclusion, a Strong argument
  •       When Premises very Unlikely imply the Conclusion, a Weak argument

o     Inductive Argument:  Adding Relevant Premises can Strengthen



Implication versus Inference


Test for Good Argument

Evaluating Premises


Claims and Our Attitudes

o     Accept as true

o     Reject as False

o     Suspend Judgment on True-Value


Basis for Our Attitude in (Usual) Descending Reliability



Arguing Backwards (Ill Advised)

o     Believe a Conclusion is True

o     Infer the Premises are True

o     All birds can fly

o     Robins are birds

o     Therefore, robins can fly


o     Find Counterexample or Exception (Rebuttal)

  •     Penguins Cannot Fly
  •       First Premise of Argument is False

o     Argument, with Valid Structure, becomes Weak because of False Premise


A Few Common Fallacies (Weak Forms of Reasoning)

o     Abusive

o     Circumstantial

o     You, Too (tu quo que)

o     Appeal to common practices

o     Appeal to common beliefs


Repairing Arguments


Some Arguments Are Worth Repairing


Principle of Rational Discussion (assume of Other & YOU)


Guide to Repairing Arguments (Adding Premises)


Two Observations